Colorized transmission electron micrograph of two mature extracellular Lassa virus particles (purple) near the periphery of a VERO E6 cell (green). A National Institutes of Health (NIH)-sponsored ...

Lassa virus (a member of the Arenavirus family) causes Lassa fever, a severe hemorrhagic disease that can be fatal and causes permanent hearing loss in up to one-third of those who contract it.

Lassa virus is endemic in West Africa, and it has a reservoir in rodents. There are an estimated 100,000 to 300,000 human infections yearly, which cause about 5,000 deaths.